It is based on the theory that Calvi did not commit suicide but was strangled on the orders of the mafia before being hanged from Blackfriars Bridge.

Three Mafiosi are awaiting trial in Rome on charges of conspiracy to murder Calvi.

'Positive'

They have been in custody since 1998, when Calvi's body was exhumed amid claims he had been strangled before being hanged.

The film also has the blessing of Calvi's widow, Clara, and his son, Carlo, who told BBC News Online: "It is positive.

"It advances the debate, not so much on the circumstances of my father's death but on the economic and political consequences of the affair."

Mr Calvi, speaking from his home in Montreal, Canada, said he was delighted that the film showed the human side of his father rather than the "cold and distant" figure which had often been portrayed.

The film opens in 120 cinemas all over Italy, but it is not clear whether it will get a wider distribution abroad.

The Vatican is reported to be furious over the film, and the Holy See's press office said it had "absolutely no comment" when asked for their reaction by BBC News Online.

Undermine communism

God's Bankers, directed by Giuseppe Ferrara, claims the Vatican was at the centre of a huge conspiracy involving drug-dealing Mafiosi, corrupt bankers and politicians, arms dealers and Freemasons.

It also suggests Pope John Paul II used mafia-tainted money to undermine communism in his native Poland and in other parts of Eastern Europe.

The events leading up to the death of Roberto Calvi are less than clear.

In 1981, Calvi, head of the Banco Ambrosiano, was jailed for four years and fined $11.7m for illegally exporting currency.

But he was freed on bail pending an appeal.

The film claims that Calvi turned to Archbishop Marcinkus for support and was allegedly given a guarantee that the debts would be covered.

But early in 1982, interest rates rose and the dollar soared in relation to the Italian lire, pushing the Banco Ambrosiano to the brink of collapse.

Hanging

It had massive debts, run up, the film says, by front companies in Latin America controlled by the Vatican Bank and the Institute for Religious Works (IOR), headed by Archbishop Marcinkus.

Then, on 18 June 1982, Calvi was found hanging from a scaffold under Blackfriars Bridge, his pockets full of bricks.

The City of London coroner recorded a verdict of suicide, although this was later overturned by the High Court, and a second inquest in 1983 recorded an open verdict.

But Mr Ferrara, who has been trying to make the film for 14 years, said it was inconceivable that, at the age of 62, Calvi could have "shinned up the scaffolding like a monkey with bricks in his pocket".

He believes Calvi was killed because he knew too much about links between the Vatican, the Sicilian Mafia and an illegal Masonic lodge known as P2, which included politicians, financiers, military and secret service officers.

Lured

The existence of P2 is established in Italian history, and its prime mover, Licio Gelli, was at one time due to be charged with conspiracy to murder Calvi.

Carlo Calvi says he believes his father was lured to London, overcome with chloroform and then strangled before being hanged from the scaffold.

Two months after Calvi's death the tottering Banco Ambrosiano finally collapsed.

The Vatican refused to admit legal responsibility for the bank's downfall but did acknowledge "moral involvement", and paid $241m to creditors.

It refused to hand over Archbishop Marcinkus to the Italian authorities, and he now works in a parish in the US.